Technical Field
This disclosure relates to fuel cells and more particularly to monitors for fuel cells. More particularly still, the disclosure relates to a fuel cell voltage monitoring arrangement.
Description of the Related Art
Fuel cells provide clean, direct current electricity by converting reactants, namely fuel (typically hydrogen) and oxidant (air or oxygen), to generate electric power and reaction products. Fuel cells generally employ an electrolyte disposed between two electrodes, namely a cathode and an anode. A catalyst typically induces the desired chemical reactions. The catalysts are typically located at the interfaces between each electrode and the adjacent electrolyte.
Fuel cells having various types of electrolytes are within the scope of consideration. Some fuel cells have solid polymer and solid oxide electrolytes, whereas others employ liquid electrolytes, etc. Fuel cell assemblies require separator plates for providing current passage and separating the fuel and oxidant reactant gases between the cells. They are disposed on each side of the electrode/electrolyte assembly of the individual fuel cell.
During operation, the output voltage of an individual fuel cell under load is generally less than one volt (e.g., 0.6-0.9 volts). Thus, in order to provide greater output voltage, it is usually necessary to stack numerous cells together and connect electrically in series to create a higher voltage fuel cell stack. Fuel cell stacks can then be further connected in series and/or parallel to form larger arrays for delivering higher voltages and/or currents.
It is conventional practice to sense or monitor the voltage of various ones, or even all, of the fuel cells in a fuel cell stack assembly in order to monitor the health, i.e., performance and/or endurance capacity, of the stack assembly as a whole, or even sub-groups or individual fuel cells within the stack assembly. Examples of such voltage monitoring arrangements are disclosed in U.S. Pat. Nos. 5,170,124; 5,763,113; 6,646,418; and 6,724,194, in which voltages sensed at individual ones of the fuel cells in a stack assembly are collectively analyzed by appropriate processing circuitry.
To provide a voltage signal associated with a particular fuel cell in the stack assembly, a voltage contact, lead, or pin, herein after typically a “lead” or “contact”, is in contact with the particular fuel cell at a discrete location therein or thereon, and acts as a sensor for that particular fuel cell. While the voltage lead of the sensor may be in contact with any of several locations in a typical fuel cell, one typical location is contact with the conductive, bipolar plate used to separate adjacent fuel cells. These separating plates may variously be identified as flow field plates, separator plates, water transfer plates, or the like, and the voltage lead is typically located at or near the corner of a generally rectangular-shaped fuel cell/separator plate. A single such lead typically serves to sense the voltage and provide the associated voltage signal for that particular cell.
While the afore-described arrangements of voltage sensors associated with fuel cells in a fuel cell stack assembly are able to reveal significant information regarding the condition of the cells and assembly, there are debilitating operating modes that these arrangements of sensors do not detect. Perhaps the most common of these debilitating modes is that of local fuel starvation. This condition may destroy cathode catalyst; but only in a very local area. A typical voltage monitor having a voltage lead at one corner of a fuel cell simply can not differentiate between this type of decay caused by local fuel starvation, which may be of sudden onset, and the more normal, gradual, and thus manageable decay caused by catalyst recrystallization, carbon corrosion and/or reversible catalyst layer wetting.
What is needed is an arrangement for the effective detection of local problems in the stack at the level of the individual fuel cell. An arrangement for the detection of local fuel starvation would be of particular benefit.